To get back to the OP's original question:
Most boats as delivered are "light in the bilge pump
department", as you put it.
Mine had one little electric pump
in the main bilge, and a manual (cranked from the cockpit) pump with selectable intake -- engine bilge or main bilge. Totally inadequate, in my opinion.
I added a Whale Supersub 1500 in the engine bilge, and put in a new pipe and through-hull out the transom, plus a big Rule
3500 in the main bilge, with new large pipe and through-hull. The big Rule
is mounted considerably higher than the regular main bilge pump
. The big Rule has an Ultra Junior float switch.
So now I have three electric
pumps plus one manual pump. That's probably enough regular DC electric
bilge pumps -- remember that every one of these must have its own through hull
and piping and so you would start to get to a ridiculous number of extra holes in the boat if you go much beyond this.
I think the biggest danger
with regular bilge pumps is that they will get clogged. If you spring some kind of leak and water
in the bilge goes up beyond its usual level, you are going to get a lot of crap floating in the bilge water, even if you think you keep your bilge pretty clean. In my experience, this will quickly clog the strainers on regular bilge pumps. My main bilge is very deep, and I cannot reach the strainers unless I dive the bilge with someone holding my ankles. I worry about this and think about some kind of serious crash pump/ trash pump which will pass solids and not clog, for this kind of case. We are discussing it in another thread.
As others have said, I would never, ever use the engine cooling
system as a bilge pump. Seems insane to me -- your engine will overheat when you get the inevitable clog, and then you are progressing fast down the cascade of failures which can sink your boat.
An engine-driven mechanical pump might be ok for some people. For me, it won't work because I have two alternators and no space on my engine. Besides that, what happens if you lose main engine power as the Bounty did? I would rather rely on my diesel generator
, which is mounted higher than my engine. If I could get a mechanical pump on that
, then this would be really cool, but I don't think it is practical within the tight-fitting sound enclosure. So probably I'm going to go with an AC powered electric submersible trash pump.
An entirely autonomous gasoline-powered trash pump might be a good solution, but presents lots of practical problems -- where to store it? How to be sure it will start if you never use it? How to be sure you have gasoline for it?
Anyway, we've got another thread going about those particular problems.
One more comment: through-hulls are mostly all the same size -- 1", 1.5", and 2", no matter what the size of the boat. A broken-off 1" through-hull will sink a smaller boat much faster than it will a bigger boat. So arguably, the bilge pump question is more and more scary, the smaller your boat is.
And one last comment: Bully to those designers who think about this question. I mean the Dashews, who designed the Sundeer boats with all the through-hulls outside of the main cabin
space behind water-tight bulkheads, and Amel, who do something similar (plus many watertight compartments). I wish all of our boats were like that.